Throughout her life, Scottish singing sensation Susan Boyle has carried the label "brain damaged". Now, in an exclusive interview with the Observer, the 52-year-old has revealed that she was misdiagnosed after complications at birth and has actually had Asperger's, a high-functioning form of autism.

Boyle, who shot to fame on Britain's Got Talent in 2009 to become one of the bestselling British female artists, received the diagnosis a year ago but has kept it secret. "It was the wrong diagnosis when I was a kid," she says. "I was told I had brain damage. I always knew it was an unfair label. Now I have a clearer understanding of what's wrong and I feel relieved and a bit more relaxed about myself."

Boyle's success has recently led to a cameo role in the festive film, The Christmas Candle, while Fox Searchlight is interested in making a film of her life story with Oscar-winner Meryl Streep in the lead role. But her achievements have sometimes been marred by reports of volatile behaviour and emotional outbursts.

Asperger's affects social interaction and communication skills, and sometimes hinders the ability to form relationships and gauge appropriate behaviour in different social contexts. Boyle, who was called "Susie Simple" while growing up in her home town of Blackburn, West Lothian, was bullied as a child because she was "different" from her classmates. Now she can give that difference a name.

"I went to seek a diagnosis from a Scottish specialist," she says. "Nobody told me to. I thought I had a more serious illness and couldn't function properly." Asperger's often creates anxiety in sufferers because of their inability to deal with situations which others take in their stride, and Boyle admits to being nervous about the consultation. But she coped well with a series of simple tests that showed her intelligence levels were not connected to her condition:"I was told my IQ was above average."

The singer has also suffered from depression and mood swings and acknowledges her own vulnerability and need for support. "I am not strong on my own," she admits. "When I have the support of people around me I am fine. I have a great team."

Despite building what she calls "the posh house" with her newfound wealth, she moved back to her late mother Bridget's terraced council house in Blackburn to "stay grounded". She was particularly close to Bridget, who died just before Boyle's rise to fame, and says she had to get social services in to help her cope after bereavement. She attributes her success to her mother: "I made a promise to my mum that I would do something with my life. Spiritually, she's with me all the time. She has had a word with someone upstairs because I wouldn't have had this otherwise."

Boyle says that her struggles growing up made her more determined to succeed but also left their mark on her. "You don't fight without some resentment."

She insists the new Asperger's diagnosis neither defines nor confines her. "It will not make any difference to my life. It's just a condition that I have to live with and work through." She hopes, though, that it will lead to people showing greater empathy and understanding towards her and her condition.

"I think people will treat me better because they will have a much greater understanding of who I am and why I do the things I do."